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The ( = 0, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, 0.4 and 0.5) nanopowders were synthesized by the hydrothermal method and then were hot-pressed into bulk alloys. The effects of secondary phase on the thermoelectric (TE) properties of were investigated. For and , both their electrical resistivity and Seebeck coefficients increase. While for , they decrease instead. The samples for have lower thermal conductivity. However, for , the thermal conductivity rises remarkably. As an overall result, the maximum value of dimensionless TE figure of merit ( ZT) reaches 1.52 at 873 K for the sample of , 36.5% higher than for the sample without . [ABSTRACT FROM AUTHOR]

In this work, BiNaBa2Co2O (=0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) ceramic samples were prepared by the conventional solid phase method. The influence of Na element doping on the thermoelectric properties of samples was investigated from 300 K to 950 K. Compared with undoped sample, the Seebeck coefficients of Na-doped samples have only a slight decrease. While, the electrical resistivity of the Na-doped samples reduces, for BiNaBa2Co2O ceramic samples with 0.15, the electrical resistivity decreases with increasing Na doping amounts due to the hole-doping effect. In addition, its temperature-dependent resistivity exhibits metallic electrical conductivity behavior. While, the samples with 0.20 exhibit semiconductor electrical conductivity behavior at the temperature range of 473-823 K, because of the significant reduction of the electrical resistivity and the slight decrease of Seebeck coefficients, the power factors of the doped samples get a significant improvement. For the most suitable doped sample BiNaBa2Co2O, its ZT value can reach a better value of 0.2 at 873 K. [ABSTRACT FROM AUTHOR]

In this paper, the influence of K element doping on the thermoelectric properties of the ( x = 0.00, 0.05, 0.10, 0.15, and 0.20) samples prepared by the solid-state reaction method were investigated from 333 K to 973 K. It was shown that due to the p-type K doping the electrical resistivity of the doped sample can be reduced remarkably as compared with the undoped sample, especially for the optimum doped sample . The Seebeck coefficients of the K doped samples have only a slight decrease as compared with the undoped sample. As a result of the remarkable reduction of the electrical resistivity the power factor of the doped sample have a significant improvement. The thermal conductivity of the samples is depressed due to the defects caused by K doping. As an overall result, the dimensionless figure of merit ( ZT) of the sample reaches a maximum value of 0.3 at 973 K, being 93% higher than that of the undoped sample. [ABSTRACT FROM AUTHOR]

Ce-doped Ce xBi2 − xTe2.7Se0.3 ( x = 0-0.3) nanopowders were synthesized by the hydrothermal method and the obtained nanopowders were hot-pressed into bulk at 673 K under a pressure of 60 MPa in vacuum. The results show that Ce doping has significant effects on the morphologies of the nanopowders. With increasing Ce doping amount the morphology of the nanopowder changes from nanosheets to nanorods. The thermoelectric (TE) properties measurements show that Ce doping can increase the electrical conductivity greatly, but has little effect on improving Seebeck coefficient and thermal conductivity. There is an optimum value of Ce doping amount. The Ce0.2Bi1.8Se0.3Te2.7 sample shows a highest figure of merit of 0.85 at 413 K as compared to other samples prepared in same conditions. [ABSTRACT FROM AUTHOR]

Ca2.7Bi0.3Co4O9 samples have been sintered in temperature range of 1183–1243 K by conventional solid-state reaction method. XRD and SEM investigations show that c-axis-oriented structure could be formed in these samples and Lotgering factors increase with the increase of sintering temperature when it is below 1223 K, from 52% for the sample sintered at 1183 K to 86% for the sample sintered at 1223 K. Due to decomposition of Ca2.7Bi0.3Co4O9, however, the c-axis-oriented structure was destroyed in the sample sintered at 1243 K although Ca2.7Bi0.3Co4 O9 phase could be recovered at the cooling stage. The size of grains in all samples increases with the increase of sintering temperature, but the relative densities are almost kept unchanged for the samples sintered at the temperature higher than 1183 K. Due to the highly textured structure, the transport properties of the sample sintered at 1223 K are anisotropic and its ZT values in the ab plane are obviously larger than those along the c-axis. [ABSTRACT FROM AUTHOR]

Ca3-xBixCo4O9(x = 0.0, 0.3) samples have been prepared at 1223 K by conventional solid-state reaction method. XRD and SEM investigations reveal that c-axis-oriented structure could be formed in Ca2.7Bi0.3 Co4O9 samples, whereas grains in Ca3Co4 O9 samples distribute randomly. Moreover, Bi doping increases the grain size and relative density of Ca2.7 Bi0.3Co4O9. The electrical conductivity along the ab plane for Ca2.7Bi0.3Co4O9 is about four times as large as that along the c-axis, but the Seebeck coefficient is almost isotropic, which leads to a remarkable rise of the power factor in ab plane for Ca2.7Bi0.3 Co4O9 compared with untextured Ca3Co4 O9. The textured structure in Ca2.7Bi0.3Co4O9 sample should be attributed to the effect of Bi doping. [ABSTRACT FROM AUTHOR]

I-doped Bi 2 Te 3−x I x (x=0, 0.05, 0.1, 0.2) flower-like nanoparticles were synthesized by a hydrothermal method through a careful adjustment of the amount of ethylenediamine tetraacetic acid surfactant. The nanopowders of flower-like nanoparticles were hot-pressed into bulk pellets and the thermoelectric properties of the pellets were investigated. The results showed that I-doping decreased the electrical resistivity effectively, and the thermal conductivitives of the Bi 2 Te 3−x I x bulk samples was lower because of the closer atomic mass of I compared to Te. As a result, a ZT value of 1.1 was attained at 448 K for the Bi 2 Te 2.9 I 0.1 sample. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of the thermoelectric materials CoSb3 and LaFe3CoSb12 were calculated by using the linearized augmented plane wave based on the density-functional theory of the first principles in order to understand why the doped compound LaFe3CoSb12 has superior thermoelectric properties than that of CoSb3. The effects of La filling in the skutterudite crystal voids and Fe substituting for Co on the electronic and thermoelectric properties were investigated by comparing the band structure, the partial density of states (PDOS), the scanning transmission microscope (STM) and the bonding orbital of CoSb3 and LaFe3CoSb12. We proposed that the enhancement of the thermoelectric properties of LaFe3CoSb12 can be attributed to its narrow energy gap, large effective mass of carriers and many extrema and obvious anisotropy existing in the band structure. The remarkable reducing of the thermal conductivity of LaFe3CoSb12 may be attributed to the weakened bonding behaviors of the covalence. [Copyright &y& Elsevier]

The thermoelectric properties of Bi 2 Ba 2 Co 2 O y and Bi 1.975 Na 0.025 Ba 2 Co 2 O y +x wt% carbon nanotubes (CNT; x=0.00, 0.05, 0.10, 0.15, 0.5, and 1.0) ceramic samples synthesised by the solid-state reaction method were investigated from 300K to 950K. Na doping with a small amount played an important role in reducing resistivity and slightly reduced the Seebeck coefficients and the thermal conductivity. The CNT dispersant increased resistivity, but the thermal conductivity was reduced remarkably. In particular, the Bi 1.975 Na 0.025 Ba 2 Co 2 O y +1.0wt% CNT sample exhibited an ultralow thermal conductivity of 0.39 W K −1 m −1 at 923K. This was attributed to the point defects caused by Na doping and the interface scattering caused by the CNT dispersant. The combination of Na doping and CNT dispersion had better effects on thermoelectric properties. The Bi 1.975 Na 0.025 Ba 2 Co 2 O y +0.5wt% CNT sample exhibited a better dimensionless figure of merit ( ZT ) value of 0.2 at 923K, which was improved by 78.2%, compared with the undoped Bi 2 Ba 2 Co 2 O y sample. [ABSTRACT FROM AUTHOR]

Abstract: Ni1−x Li x O (x =0, 0.03, 0.06, 0.09) powders were prepared by sol–gel method combined with sintering procedure using Ni(CH3COO)2·4H2O and citric acid as the raw materials and alcohol as solvent. The crystal structures of the samples were investigated by X-ray diffraction and Raman spectroscopy. The thermoelectric properties, such as the electrical conductivity, the Seebeck coefficient and the thermal conductivity were measured. The results showed that all the samples are p-type semiconductors. The electrical conductivity increases with the increase of the temperature, which indicates that the substitution of Li+ for Ni2+ can increase the concentrations and mobility of the carriers. The thermal conductivity decreases remarkably with the increase of the Li doping content, which indicates that Li doping can enhance the scattering of phonon. However, the Seebeck coefficient will decline with the increase of the Li doping content. As results of the increase of electrical conductivity and reduction of thermal conductivity, Li doping can increase the figure of merit (ZT) of NiO, the ZT value reach 0.049 at 770K for Ni1−x Li x O with x =0.06. [Copyright &y& Elsevier]

Abstract: Nanostructure engineering and rare earths filling were employed to enhance the thermoelectric properties of the CoSb3 based skutterudite. The CoSb3 and the rare earths filled LaFe3CoSb12, CeFe3CoSb12, La0.5Ce0.5Fe3CoSb12 nano-powders were prepared via a hydro/solvo thermal method and then the nano-powders were used to make bulk samples by hot-press. Our results indicate that besides the nanostructure and the rare earths filling, the existence of a glassy phase in the samples is also an important factor for the enhancement of the thermoelectric properties. The Seebeck coefficients of the samples were improved obviously while their excellent electrical conductivities could be maintained, meanwhile the thermal conductivities of the samples were suppressed significantly. Therefore, the figures of merit were enhanced and ZT values could be reached at 773K as 0.19, 0.43, 0.62 and 0.82 for CoSb3, LaFe3CoSb12, CeFe3CoSb12 and La0.5Ce0.5Fe3CoSb12 respectively. [ABSTRACT FROM AUTHOR]

Ca2.7Bi0.3Co4O9 samples have been sintered in temperature range of 1183–1243 K by conventional solid-state reaction method. XRD and SEM investigations show that c-axis-oriented structure could be formed in these samples and Lotgering factors increase with the increase of sintering temperature when it is below 1223 K, from 52% for the sample sintered at 1183 K to 86% for the sample sintered at 1223 K. Due to decomposition of Ca2.7Bi0.3Co4O9, however, the c-axis-oriented structure was destroyed in the sample sintered at 1243 K although Ca2.7Bi0.3Co4 O9 phase could be recovered at the cooling stage. The size of grains in all samples increases with the increase of sintering temperature, but the relative densities are almost kept unchanged for the samples sintered at the temperature higher than 1183 K. Due to the highly textured structure, the transport properties of the sample sintered at 1223 K are anisotropic and its ZT values in the ab plane are obviously larger than those along the c-axis. [ABSTRACT FROM AUTHOR]

Abstract: The electrical resistivity and Seebeck coefficients of RBaCo4O7 (R=Dy, Ho, Y and Er) were measured in the temperature range 350–1000K. It was found that all compositions behave as p-type semiconductors in the temperature range measured. The calculated activation energy of conductivity is larger than that of thermopower in the temperature range of 350–650K, which means that the conduction mechanism may be determined as a small polaron hopping model. The conduction mechanism may be changed when temperature is above 650K due to a possible change in symmetry or/and the release of oxygen from crystal lattices. The power factors (S 2/ρ) increase with the increase of temperature and the maximum value of YBaCo4O7 at 1000K is 4.9×10−5 Wm−1 K−2 that is comparable to that of Ca3Co4O9. [Copyright &y& Elsevier]